JrJackson compatibility issue with 9000

[nirvdrum]

JrJackson currently doesn't work with the 9000-dev builds because it uses a JRuby API that was removed. Relevant trace:

     Failure/Error: Unable to find matching line from backtrace
     Java::JavaLang::NoSuchMethodError:
       org.jruby.javasupport.util.RuntimeHelpers.constructHash(Lorg/jruby/Ruby;Lorg/jruby/runtime/builtin/IRubyObject;Lorg/jruby/runtime/builtin/IRubyObject;Lorg/jruby/runtime/builtin/IRubyObject;Lorg/jruby/runtime/builtin/IRubyObject;)Lorg/jruby/RubyHash;
     # com.jrjackson.RubyObjectDeserializer.mapObject(RubyObjectDeserializer.java:180)
     # com.jrjackson.RubyObjectDeserializer.deserialize(RubyObjectDeserializer.java:65)
     # com.jrjackson.RubyObjectDeserializer.deserialize(RubyObjectDeserializer.java:20)
     # com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
     # com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2103)
     # com.jrjackson.JrJacksonRaw._parse(JrJacksonRaw.java:105)
     # com.jrjackson.JrJacksonRaw.parse_sym(JrJacksonRaw.java:87)
     # com.jrjackson.JrJacksonRaw$INVOKER$s$1$0$parse_sym.call(JrJacksonRaw$INVOKER$s$1$0$parse_sym.gen)

[nirvdrum]

This was fixed some time ago in master.